It is known in the art that nylon, such as nylon 66, can be produced in a multi-step process. In the first step, butadiene (BD) is hydrocyanated with hydrogen cyanide (HCN) in the presence of a homogeneous nickel catalyst to produce adiponitrile (ADN). Subsequently, organic impurities are removed from the ADN to make a refined ADN. Suitable methods for removing the organic impurities include extraction and distillation. See Ostermaier, U.S. Pat. No. 6,331,651, incorporated herein by reference. In the next step, the refined ADN is catalytically hydrogenated to produce HMD or mixtures comprising ACN and HMD. Suitable hydrogenation catalysts include iron-based and Raney type heterogeneous catalysts, such as Raney nickel. In subsequent steps, ACN and HMD are used in the manufacture nylon polymers, such as nylon 6 and nylon 66.
The ADN made in this process contains several impurities that may have an adverse effect on the hydrogenation of the ADN to ACN and HMD. The impurities include: phosphorous (III) compounds (the “P(III) compounds”); 2-cyanocyclopentylideneimine (CPI); and tert-butyl catechol (TBC).
The P(III) compounds are adsorbed on the surface of heterogeneous catalysts and cause poisoning and subsequent deactivation of the iron-based catalyst.
The CPI is hydrogenated to aminomethylcyclopentylamine (AMC) during the hydrogenation of the ADN. The AMC is difficult to separate from the HMD and causes degradation of polymer quality when the HMD is converted to nylon 66 polymer.
The removal of some of these impurities has been addressed in the past. For example, U.S. Pat. No. 6,331,651 (“'651 Patent”) describes the ADN which contains P(III) compounds, which is treated with air containing greater than 0.1% wt. ozone in a reactor which provides rapid mass transfer rates, such as an agitated tank fitted with a gas sparger, a pipeline reactor fitted with a static mixer, a tank fitted with a jet mixer or an absorption column. The '651 patent states that it is believed that the P(III) compounds are converted by the ozone treatment to phosphorous compounds in the +5 oxidation state, which are less injurious to the iron-containing hydrogenation catalyst.
Canadian patent 672,712 describes a process for purifying ADN containing impurities, which can be made by several different processes. One of the identified impurities is CPI. The process comprises contacting the ADN with gaseous ozone at a temperature of between 0 and 110° C., preferably 20-50° C.
U.S. Pat. No. 6,359,178 discloses a process for producing hexamethylene diamine (HMD) by hydrogenating adiponitrile, wherein the ADN recycle stream is purified in a conventional manner, such as treatment with an inorganic acid, an organic acid, an acidic ion exchanger or by treatment with an oxidizing agent such as air, ozone or hydrogen peroxide.
USSR Patent Publication 276033 discusses purification of ADN by contacting it in a vessel with an ozonized air, optionally in the presence of an acid, such as phosphoric acid.
Fisher et al., WO 00/03972, disclose the production of HMD, wherein the recycle of ADN is cleaned in a known manner, e.g., by treatment with an inorganic or organic acid, or an oxidizing agent, such as air, ozone, hydrogen peroxide or an inorganic or organic peroxide.
Heckle, U.S. Pat. No. 4,952,541; Yamada et al U.S. Pat. No. 3,725,459; Pounder et al. U.S. Pat. No. 3,758,545; Nishimura et al., U.S. Pat. No. 3,803,206, disclose different processes for purification of adiponitrile and acrylonitrile or reactants used in such processes.
Nonetheless a need still exists for an improved process using ozone to reduce or eliminate problems associated with impurities in ADN.